Hybrid vehicle powertrains utilize electrically-variable transmissions that combine the use of electric motors and conventional engine power to produce a more efficient vehicle via: (i) engine start-stop operation; (ii) more efficient engine operating points; and (iii) recapture of vehicle kinetic energy into a storage battery by means of regenerative braking. Some hybrid powertrains have an “input-split” architecture, whereby the engine power is split between a direct mechanical connection to the output wheels and an electric generator, with the latter both charging the onboard battery and/or delivering power to a motor connected to the output wheels. Operation with such a powerflow arrangement is referred to as an input-split operating mode. The transmission also functions as an electrically variable transmission (EVT), enabling more optimal engine operating speed and load. Some EVTs offer two EVT modes, as well as a number of fixed gear ratios, as in a conventional automatic transmission.
The intended operating mode of the aforementioned architectures is to blend the use of the conventional engine and electric motor/generators in the most efficient way possible. Therefore, unlike a purpose-built electric vehicle (EV), input-split EVT architectures are not designed to operate for an extended period of time using only battery power, and consequently are not as efficient in such an electric-only operating mode.